CN106441511B - Discrete liquid level sensor based on fiber Bragg grating technology - Google Patents
Discrete liquid level sensor based on fiber Bragg grating technology Download PDFInfo
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Abstract
A kind of discrete liquid level sensor based on fiber Bragg grating technology, including wideband light source, 3dB fiber coupler, FBG sensor array, Wavelength demodulation module and micro control unit.The light of wideband light source output is through 3dB fiber coupler, and successively by the temperature reference grating and stress sensing grating that are adhered on cantilever beam structure in FBG sensor array, encapsulating material, float material and the grating adhesion material of sensing probe are carbon fiber；Liquid level variation can change on float that magnet is to the active force of iron plate on carbon fiber board, and making carbon fiber board, deformation occurs, to change the reflection wavelength of sensing grating, for the light of reflection through 3dB fiber coupler, input wavelength demodulation module completes the demodulation of reflection wavelength；Then it transfers signals to the micro control unit with Temperature-Stress backoff algorithm and carries out data processing.The configuration of the present invention is simple is reliable, detection accuracy is high, high sensitivity, can be applied to the adverse circumstances such as high temperature, high corrosion, realizes the noncontinuity detection of the liquid level of different height.
Description
Technical field
The present invention relates to a kind of discrete level monitoring sensors, are based on fiber bragg grating more particularly to one kind
The liquid level sensor that can be applied under adverse circumstances of technology and contactless cantilever beam mechanical structure.
Background technique
Level monitoring is one of groundwork of process control, and liquid level sensor is the device for detecting liquid height, it
Have important in the production of daily life and modernization and is widely applied.With intelligent, unitized, the liquid level of control system
The object of measurement is also further extensively, it is desirable that the measurement accuracy of liquid level sensor is higher, better reliability, practicability are stronger and more
Add and is suitable for special measurement environment.Especially when there is measured medium viscosity, electric conductivity or liquid level to have fluctuation or exist
Bubble, or need to consider whether the airtightness of container and liquid have situations such as corrosivity, toxicity and explosion hazard, selection is suitable
Level measuring technology it is particularly important.
Currently, main discrete level measuring method mainly have electric pole type level gauging, calorifics formula level gauging and
Total-reflection type level gauging based on light.Wherein, electric pole type level gauging is led by what liquid contact with two electrodes was constituted
The detection of liquid level is realized in logical circuit, and this method is simple, cheap, but may not apply to the level gauging of megohmite insulant, easily
By electromagnetic interference influence；Calorifics formula level gauging is the difference that environment temperature and fluid temperature are detected by thermistor, dress
Set small and exquisite, but when environment temperature is close with fluid temperature, detection resolution is low, and measurement effect is poor；With domestic patent of invention
For number for the patent of invention of CN101140181A, the total-reflection type level measuring method based on light is using reflected light or transmission
Light carries out the detection of liquid level, such sensor contains light source and optical receiver simultaneously, the light that light source issues is incident on prism
Or in optical fiber, the front-end architecture of sensor is constituted.In the presence of not having liquid, the light that light source issues is by prism or fiber reflection
Into receiver, when liquid-immersed prism or optical fiber, the light that light source issues is refracted into liquid by prism or optical fiber, only very
It is few to be reflected in receiver even without light, the variation of optical power under above situation is detected by receiver, to drive electricity
Sub switch or control circuit are to realize warning function.Because most of all using optical fiber or prism end as sensing in the technology
Probe removes contact liq, exposed sensing probe may be subjected to floating material, vibration, filling generation dynamic disturbance influence,
In addition, sensor needs daily maintenance, and heavy workload increases due to the biological attachment or chemical contamination of optical fiber or prism surface
Add.
A kind of sensing responsive element of the bragg grating (FBG) as superior performance, compared with traditional sensor,
Sensing technology is relatively new, fiber grating small volume, high sensitivity and not by electromagnetic interference.It is managed according to fiber grating coupled mode
By it is found that FBG is to form a narrow band filter and reflecting mirror in fibre core, to the spectrum being incident on grating carry out reflection and
Transmission.When FBG is strained and temperature influences, bragg wavelength can shift, can benefit by the introducing of mechanical sensitivity device
With physical quantitys such as optical fiber grating measuring pressure, vibrations；If the variation of set environment liquid level influences the variation of above-mentioned physical quantity, knot
The wavelength reflection modulation principle for closing fiber grating can realize the indirect measurement of liquid level, have preferable structure and theoretical novelty,
And there is stronger practical value.
Summary of the invention
In order to overcome the above-mentioned deficiencies of the prior art, the invention proposes a kind of based on the non-of fiber Bragg grating technology
Continuous type liquid level sensor.Pass through the application of fiber Bragg grating technology and the design of contactless cantilever beam mechanical structure
The noncontinuity level gauging under adverse circumstances can be achieved, the present invention has stable mechanical structure, higher sensitivity and good
Good detection performance.
The technical scheme adopted by the invention is that: a kind of discrete level sensing based on fiber Bragg grating technology
Device as shown in Figure 1, its main feature is that: including wideband light source, the 3dB fiber coupler being connect with the output end of wideband light source, with 3dB
The FBG sensing probe of fiber coupler output end connection, the Wavelength demodulation module being connect with 3dB fiber coupler light echo end, with
The micro control unit of Wavelength demodulation module connection.The 3dB fiber coupler of the sensor can also be replaced by circulator, can pass through wavelength-division
Multiplexing technology (WDM), time-division multiplex technology (TDM) or space division multiplexing technology (SDM) realize the multiplexing of multiple sensors, to realize
The noncontinuity of different height liquid level measures.
A kind of discrete liquid level sensor based on fiber Bragg grating technology, the output light of the wideband light source
Spectrum has fabulous flatness, covers the reflectance spectrum of sensing probe internal stress sensing grating and temperature reference grating, while light source
Automatic temperature-adjusting control (ATC) circuit and automated power control (APC) circuit with very high degree of precision are to maintain the height of light source working
Stability and high reliability.
A kind of discrete liquid level sensor based on fiber Bragg grating technology, relates to setting for FBG sensing probe
Meter, structure is as shown in Fig. 2, include FBG sensor and float two parts.FBG sensor uses cantilever beam mechanical structure, special
Point is: the temperature reference light for being placed in carbon fiber board stent area including being fixed on carbon fiber board and relaxation on cantilever beam support
Grid and the strain sensing grating and iron plate for being fixed on the hanging region of carbon fiber board.Float material is carbon fiber, is partially submerged into thereon
Magnet；Its position is limited by float limited block, can be to avoid float to biography in this way when liquid level is more than device detection range
Photosensitive grid damage.
A kind of discrete liquid level sensor based on fiber Bragg grating technology, the Wavelength demodulation module use
Tunable fiber Fabry-Perot(F-P) filter method realizes temperature reference grating and strain sensing optical grating reflection central wavelength
High-precision demodulates.
A kind of discrete liquid level sensor based on fiber Bragg grating technology, the micro control unit is according to wavelength
The real time data and sensor-based system that demodulation module provides originate nominal data, realize wavelength variable quantity and microstrain, microstrain
With the conversion of liquid level, early warning differentiation is finally carried out according to surveyed level value, to decide whether to start early warning control circuit.
Compared with existing discrete liquid level sensor, the present invention is had the advantage that
(1) with many advantages sensing technology, the sensor based on FBG technology have stability is good, detection accuracy is high,
The advantages that high sensitivity, low in energy consumption, electromagnetism interference.
(2) homemade sensing probe structure is simple, size is smaller, low cost, is easily installed and fault detection, unique machine
The design of tool structure makes liquid be not directly contacted with sensing element and realize level gauging.
(3) encapsulating material of sensing probe, float material and grating adhesion material are carbon fiber, have probe resistance to
The good characteristics such as high temperature, corrosion-resistant, wear-resisting, stretch-proof and shock resistance.
(4) multiplexing of multiple sensing probes can carry out the level sensing of plurality of liquid or different height simultaneously.
Detailed description of the invention
Fig. 1 is the discrete liquid level sensor structure chart based on fiber Bragg grating technology.
Fig. 2 is FBG sensing probe structure chart.
Fig. 3 is multiple FBG sensing probe assembling assumption diagrams.
Fig. 4 is four-way liquid level sensor system structure chart.
Specific embodiment
The Bragg equation of fiber grating isλ= 2 n eff Λ, the center reflection wavelength of fiber bragg gratingλIt can be with
Screen periodsΛWith fibre core effective refractive indexn eff Variation and change.When effects of strain or surrounding of the FBG by longitudinal direction
When temperature changes,ΛWithn eff Size can change, shift so as to cause grating Bragg central wavelengthdλ=2 n eff dΛ+2Λdn eff 。
It is sensed in a kind of discrete liquid level sensor based on fiber Bragg grating technology for the FBG of level sensing
Sonde configuration is as shown in Fig. 2, the FBG sensor signal for illustrating the internal float schematic diagram equipped with magnet and being placed in encapsulating shell
Figure.FBG sensor is made of fiber bragg grating cantilever beam structure, and when liquid level rises, float is also therewith to moving up
Dynamic, the magnet in float attracts the carbon fiber board with iron sheet at this time.The bending of carbon fiber board makes to adhere to Prague thereon
Strain sensing grating strains, and then the strain sensing grating wavelength of FBG sensor shifts.On the contrary, if float with
Liquid level decline moves down, and the magnetic force acted on cantilever beam iron sheet will reduce, and cantilever beam is then restored to original position naturally
It sets, then the wavelength of Bragg grating is also moved back into initial value.
Theoretically, the response sensitivity that grating is generated by the stress being applied to it can state are as follows:Δλ = λG ε
ε, whereinΔλIt is drift of the FBG due to the central wavelength generated by stress,λIt is the bragg wavelength of FBG,G ε It is
The axial strain coefficient of optical fiber, ε are corresponding variables.For example, when bragg wavelength is 1550nm, GεFor quartz silica light
Fibre is 0.78, and the coefficient of strain of wavelength is 1.2pm/ μ ε.Therefore, when applying 1000 μ ε to FBG sensor, its wavelength can be generated
The variable quantity of 1.2nm.
In design, the wavelength of strain sensing grating can be influenced by stress and temperature simultaneously, therefore temperature reference grating
It needs to carry out strain isolating, is affected by temperature its wavelength only.In implementation, the relaxation of temperature reference grating is placed in carbon fiber by us
Board mount region is tieed up, strain sensing grating both ends are fixed on to the hanging region of carbon fiber board, the grating of two wavelength is utilized
WDM realizes the multiplexing of stress and temperature grating, to distinguish the reflected different waves for carrying temperature and strain information
Then long optical signal transfers signals to the micro control unit with temperature stress backoff algorithm and carries out data processing, to realize
To in stress sensing grating the wavelength change as caused by temperature carry out temperature-compensating, then by obtained level value with set in advance
The threshold value set compares, to determine whether that outwardly system sends pre-warning signal to drive control circuit.
As shown in figure 3, in order to monitor different liquid levels, by the way that multiple optical fiber sensing probes are encapsulated in a carbon fiber
It is made into a sensor array in dimension pipe, optical signal is transmitted using an optical cable, passes through operating wave in entire sensor array
Long difference encodes to realize to pop one's head in.
Fig. 4 is four-way liquid level sensor system structure chart, (central wavelength 1550nm, bandwidth after light is issued by wideband light source
40nm, optical power 20mW), it injects in 1 × 4 fiber coupler, by the quartering, each section light all passes through the light of injection
It is transferred to after 3dB fiber coupler in the grating sensing probe with different central wavelengths；Reflected light wave passes through 3dB light
Reflected optical signal is integrated together by another 1 × 4 fiber coupler again after fine coupler；Light after integration
Signal is transferred to Wavelength demodulation module again, demodulates to the wavelength of each peak power；Then obtained data are transmitted
To the micro control unit for having temperature compensation algorithm, the measurement and early warning of different liquid levels are finally realized.
Claims (5)
1. a kind of discrete liquid level sensor based on fiber Bragg grating technology, characterized in that including wideband light source, with
One 1 × 4 fiber coupler of the output end connection of wideband light source, the 3dB being connect with 1 × 4 fiber coupler output end
Fiber coupler, the FBG sensing probe connecting with 3dB fiber coupler output end are connect with 3dB fiber coupler light echo end
Another 1 × 4 fiber coupler, the Wavelength demodulation module being connect with another 1 × 4 fiber coupler output end, with wavelength solution
The micro control unit of mode transfer block connection realizes that FBG sensing is visited by wavelength-division multiplex technique, time-division multiplex technology or space division multiplexing technology
The multiplexing of head, multiple FBG sensing probes are encapsulated in a carbon fiber pipe, are formed sensor array, are carried out different liquid levels
Noncontinuity measurement；
After light is issued by wideband light source, inject in 1 × 4 fiber coupler, the light of injection is by more equal parts, and each section light is all
By being transferred to after 3dB fiber coupler in the FBG sensing probe with different central wavelengths；Reflected light wave passes through
Reflected optical signal is integrated together by another 1 × 4 fiber coupler again after 3dB fiber coupler；After integration
Optical signal be transferred to Wavelength demodulation module again, the wavelength of each peak power is demodulated, by obtained data transmit
To the micro control unit for having temperature compensation algorithm, the measurement and early warning of different liquid levels are realized；
The FBG sensing probe includes FBG sensor, float and package tube three parts；The FBG sensor uses cantilever
Beam mechanical structure, the temperature for being placed in carbon fiber board supporting zone including being fixed on carbon fiber board and relaxation on cantilever beam support
Reference grating and the strain sensing grating and iron plate for being fixed on the hanging region of carbon fiber board, the float material are polyacrylonitrile-radical
Carbon fibers Carbon fibers, are above partially submerged into samarium cobalt magnet, and float position is limited by float limited block.
2. the discrete liquid level sensor according to claim 1 based on fiber Bragg grating technology, characterized in that
The 3dB fiber coupler can be replaced by circulator.
3. the discrete liquid level sensor according to claim 1 based on fiber Bragg grating technology, characterized in that
The center reflection wavelength of the temperature reference grating is different from the center reflection wavelength of strain sensing grating.
4. the discrete liquid level sensor according to claim 1 based on fiber Bragg grating technology, characterized in that
The carbon fiber board with a thickness of 0.5-2mm.
5. the discrete liquid level sensor according to claim 1 based on fiber Bragg grating technology, characterized in that
The Wavelength demodulation module is that the demodulation of wavelength is realized using tunable Fabry-Perot filter method.
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